CROSS-REFERENCE TO RELATED APPLICATIONS
FIELD OF THE INVENTION
This application claims priority from application Ser. No. 10/351,649, filed Jan. 23, 2003, now pending, which claims priority from application Ser. No. 09/822,962, filed Mar. 30, 2001,now pending, which claims priority from provisional application serial No. 60/203,222, filed May 5, 2000, abandoned.
- BACKGROUND OF THE INVENTION
Jet engines can produce a high noise level if the velocity of the mass flow exiting the engine is non-uniform and high. For performance considerations, jet engines often have multiple nozzles with the mass flow exiting each nozzle at a different velocity. Since noise radiating from a jet's exhaust increases with the intensity and non-uniformity of the exhaust velocity, jet noise reduction concepts have historically focused on methods for rapidly mixing the flows and achieving a uniform velocity within a short distance of the nozzles.
Various flow-mixing devices have been employed in the past to achieve a uniform velocity within a jet's exhaust and to reduce the noise radiated from the exhaust flow. While those devices have been successful at reducing jet noise, the thrust, drag, and weight penalty associated with those devices have often been of a magnitude that the noise at constant aircraft performance has not been reduced. During the NASA Advanced Subsonic Transport (AST) Program (reference 1) sharp pointed, triangular shaped, extensions added to the sleeve of an external plug primary nozzle were tested and were found to reduce jet noise. A. D. Young et al (U.S. Pat. No. 3,153,319, reference 2) also developed extensions that when added to the trailing edge of nozzles reduced jet noise.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The primary difference between the above-described prior art and the hereinafter described invention is the rounding of the upstream intersection of the extensions with the nozzle and the rounding of the extension's trailing edge. Rounding has been found to enhance the reduction of low frequency noise while inhibiting an increase in high frequency noise. Increased high frequency noise has been a characteristic of the previous sharp edged devices even though they have reduced low frequency noise and have had a net acoustic benefit. Rounding has also been found to reduce the thrust loss of the previous sharp edged devices.
FIG. 1 is a perspective view of a jet engine segmented mixing device with external plug nacelle;
FIG. 2 is illustrative of a jet engine segmented mixing device with internal plug nacelle;
FIG. 3 is illustrative of a jet engine segmented mixing device with mixed flow nacelle;
FIG. 4 is a triangular planform showing of a segmented mixing device on a nozzle sleeve;
FIG. 4A is a sectional view, taken along the lines 4A-4A of FIG. 4, showing in more detail how the surfaces of the mixing device extensions curve inward towards the engine center line;
FIG. 4B is a sectional view, taken along the lines 4B-4B of FIG. 4, showing in more detail how the extensions create a stream wise vortex;
FIG. 5 is a trapezoidal planform showing of a segmented mixing device on a nozzle sleeve;
FIG. 6 is illustrative of stream wise vortex flow;
FIG. 7 is illustrative of a jet engine with a segmented mixing device attached to a core compartment vent;
DETAILED DESCRIPTION OF THE INVENTION
FIG. 8 is illustrative of an aircraft wing with a segmented mixing device in the slot between fore and aft airfoils.
The present invention comprises a segmented mixing device which, when applied to the nozzle of a jet engine or surfaces of an aircraft, enhances mixing between adjacent flows and reduces the noise radiated from the jet's exhaust flow and the flow adjacent to the devices on the aircraft. The device does so with a very small degradation in aircraft performance when attached to the jet's primary nozzles. When the device is attached to secondary nozzles or vents or slotted airfoils, an improvement in engine or aircraft performance can result. The mixing device is a segmented, triangular or trapezoidal shaped, curved extension 1 to a nozzle's sleeve or surface trailing edge which results in a serrated trailing edge (see FIGS. 1, 2, 3, 7, and 8). This invention comprises: 1) A modification from the sharp pointed, triangular shaped, nozzle extensions evaluated in the hereinafter referenced NASA AST program to a semi-round, triangular or trapezoidal shaped planform (see FIGS. 4 and 5). 2) An application of the present nozzle extensions to internal and external plug primary nozzles of dual flow exhaust systems (see FIGS. 1 and 2). 3) An application of the nozzle extensions to secondary nozzles of dual flow exhaust systems (see FIGS. 1 and 2). 4) An application of the nozzle extensions to the nozzle of mixed flow exhaust systems and the flow splitter between the primary and secondary streams of those systems (see FIG. 3). 5) An application of the nozzle or surface extensions to vents in exhaust systems (see FIG. 7). And, 6) an application of the surface extensions to the trailing edge of any surface separating adjacent flows wherein enhanced mixing is desired (as an example, see FIG. 8).
The purpose of the present nozzle or surface extensions 1 is to enhance the natural free mixing of the adjacent flows and to reduce the acoustic energy associated with the velocity differences between the streams in which they are imbedded. The presently configured nozzle or surface extensions enhance the natural free mixing between adjacent streams by forcing the adjacent flows to penetrate into one another to a greater depth than that achievable with free mixing and therefore results in a more uniform flow in a shorter stream wise distance. The acoustic benefit of the extensions increases as the velocity differences between the streams increase. Two methodologies are employed to enhance mixing: 1) The surfaces of the extensions curve inward towards the engine centerline forcing the secondary (outer) flow into the primary (inner) flow (see FIG. 4A). 2) The extensions have a planform shape that creates a stream wise vortex that also enhances rapid mixing of the two streams (see FIG. 4B and FIG. 6). For extensions attached to nozzles, the circumferential shape of the extension's surface is an arc with a radius equal to the distance from the nozzle centerline to the extension's surface, i.e. an axisymetric surface (see FIG. 4B). Outward turned segments can also be used to enhance mixing. However, the thrust loss for outward turned segments on nozzles has been greater than that for inward turned segments. The present concept also includes rounding to outward turned segments.
Unlike the previous NASA AST configurations and the A. D. Young et al configurations described in U.S. Pat. No. 3,153,319, the extensions defined herein incorporate a planform with semi-rounded intersections 2 with the baseline nozzle and semi-round trailing edges 3. The purpose of the upstream rounding is to increase the strength of the stream wise vortex by allowing the primary (inner) flow to exit the nozzle sooner and in a more radial manner. Rounding the upstream intersection also eliminates the stress concentrations and low fatigue life of the previous NASA AST and A. D. Young et al concepts. Rounding the extension's trailing edge separates the two stream wise vortexes and increases the circumferential surface area available for the secondary (outer) flow to penetrate the primary (inner) flow. In addition, rounding the trailing edge increases the span-wise average turning angle, 0 (see FIG. 4A), of the secondary flow resulting in greater penetration of the secondary flow into the primary flow and increased mixing of the two flows. Rounding has been found to enhance the reduction of low frequency noise while inhibiting an increase in high frequency noise. The increase in high frequency noise has been a characteristic of the previous designs. Rounding has also been found to reduce the thrust loss of sharp pointed or small radiused nozzle extensions. The nozzle or surface extensions may vary in length, width, curvature, and count being only constrained by the geometry of the baseline nozzle or the surface to which they are attached.
In addition to using segmented surface extensions to reduce noise, they can be used to reduce drag on surfaces downstream of the segments when those surfaces are scrubbed by the flow that is adjacent to the segments. This is especially beneficial when the flow scrubbing the downstream surface has the lower energy level of the two adjacent flows. The drag reduction is achieved through mixing of the flows adjacent to the segments and the action of the vortexes emanating from the segments. Mixing increases the energy level (total pressure) of the flow having the lowest energy adjacent to the segments. The segmented extensions mix the two flows more rapidly than that achieved with natural free mixing. The enhanced mixing energizes the low energy flow so that it can overcome adverse pressure gradients on the downstream surface. One example of such an application is the flow exiting the core compartment of a jet engine (see FIG. 7). Typically, core compartment flow has a low total pressure relative to ambient, exits through a vent (nozzle), and separates from downstream surfaces when those surfaces encounter higher than ambient pressures. By attaching segments to the outer surface of the vent, the core compartment flow can mix with the adjacent high-energy flow, typically fan flow, and achieve a higher energy (total pressure) in a much shorter distance from the vent than that achieved by natural free mixing. As a result, flow separation on the downstream surface is prevented. Aircraft wings incorporating slots 5 or flaps 6 is another application where drag benefits can be achieved by incorporating segmented surface extensions 1 into the slot between the fore 7 and aft 6 airfoil (see FIG. 8). The vortexes shed from the segments attached to the trailing edge of the upstream airfoil along with the energized slot flow can prevent or delay separation on the aft airfoil, reducing the drag and increasing the lift of the wing. On multi-slotted airfoils, the segmented surface extensions can be incorporated into each slot.
The segmented extension creates vortexes by immersing the tip of the extension into the adjacent flow, a methodology for creating vortexes to mix flow and reduce noise and drag. In addition, the segmented nozzles described herein are cheaper to construct than nozzles of prior art since they can be axisymetric.
1. D. C. Kenzakowski, J. Shipman, S. M. Dash, J. E. Bridges, and N. H. Saiyed, AIAA-2000-0219, “Turbulence Model Study of Laboratory Jets with Mixing Enhancements for Noise Reduction”, January 2000.
2. A. D. Young et al, U.S. Pat. No. 3,153,319, “Jet Noise Suppression Means”, Oct. 20, 1964.